148 



THE MIDDLE PAST. 



the oolite, but with new and peculiar genera of the same 

 great divisions; while for the first time the ctenoids and 

 cycloids, which are now the prevailing orders of ichthyic 

 life, make their first appearance. Among the placoids, as 

 indicating their fossil teeth, ptychodits, hybodus, acrodus, and 

 lamna are the dominant genera ; among the ganoids, gyro- 

 das, pycnodw, and macropoma; while the cycloids show 

 osmeroides, hypsodus, saurocephalus, and the like ; and the 

 ctenoids, the perch-like forms of beryx and berycopsis. 



CRETACEOUS FISHES. 



1, Baryx Lewesiensis ; 2, Osmeroides Mantelli MANTELL. 



When we turn to the reptiles, a few species of plesiosaurus 

 and ichthyosaurus still linger in the ocean j a solitary 

 iyuanodon represents the gigantic land-tribes ; and ptero- 

 dactyles, in lessening flocks, wing the sea-cliffs or skim the 

 surface of the creeks and river-mouths. The crocodiles, 



